About one child in 150 develops autism or a related disorder like Asperger’s syndrome by the age of 8, according to a study released yesterday by the Centers for Disease Control and Prevention.
The study, which looked at cases of so-called autism spectrum disorders in 14 states in 2000 and 2002, is the most rigorous analysis to date of the disorders’ prevalence in the United States. It confirms recent estimates, which put the number at roughly one in 160 children — higher than the one-in-200 estimate made in the 1980s.
The analysis also found that delays in diagnosis were common: an average of at least a year and a half from the time parents first reported odd speech problems or other social deficits, typically around the age of 3.
Children with classic autism have disabling difficulties in communicating, forming relationships and adjusting to change; those with other disorders on the spectrum have social difficulties generally less severe, and in some cases mild. Extrapolating from the number of cases it found, the study suggested that some 560,000 Americans age 21 or under struggled with such disorders.
Researchers say that both genetic variation and developmental factors combine to cause the disorders, but know little more than that.
And the new numbers are not likely to settle the continuing debates about whether there has been a true rise in autism and, if so, the underlying causes of that increase.
“Our estimates are becoming better and more consistent, though we can’t yet tell if there is a true increase in autism spectrum disorders or if the changes are the result of our better studies,” the disease centers’ director, Dr. Julie L. Gerberding, said in a statement. “We do know, however, that these disorders are affecting too many children.”
Dr. Fred R. Volkmar, director of the Child Study Center at Yale University School of Medicine, said, “It appears that the rates are unchanged over the past 20 years or so, but it is important to track these numbers.”
The researchers made their estimates on the basis of a detailed review of records from schools and health clinics in six states in 2000 and 2002, and from an additional eight states in 2002 alone. They looked at behavior problems in 8-year-olds, who are at an age by which the disorders usually become apparent.
The investigators found similar rates in most of the states surveyed, with two exceptions. The prevalence was lowest in Alabama, at one in 300, and highest in New Jersey, at some one in 100. Dr. Catherine Rice, the C.D.C. researcher who led the study, said it was likely that the Alabama number was an underestimate, because the researchers did not have access to school records in that state. The higher rate in New Jersey may reflect other differences, experts said, including a higher level of awareness and wider availability of services in communities and schools.
“We did find that there were more evaluations done in New Jersey, that kids were more likely to have an evaluation, and to have more of them, and that families had more information about these disorders,” Dr. Rice said. “But that didn’t completely explain the higher rate. At this point we really don’t have answers, but we believe the range of prevalence from 5 to 10 per 1,000 across all the states is an accurate one.”
The C.D.C. analysis involved these states: Alabama, Arizona, Arkansas, Colorado, Georgia, Maryland, Missouri, New Jersey, North Carolina, Pennsylvania, South Carolina, Utah, West Virginia and Wisconsin.
